Remote copy system

ABSTRACT

In a system in which data employed by a computer is stored in a storage system, the storage system transfers this data to another storage system and a copy of the data is maintained in the other storage system, consistency of the copy is maintained even in the case of data written to the storage system by a computer, to which a write time is not applied. A source storage system, when a write time is applied to a write request, records the write time and applies this write time to the received write data and, when no write time is applied, applies the recorded write time to the received write data and transfers the write data with this write time applied thereto, to another storage system. The target storage system stores the write data in a logical volume in the target storage system in accordance with the write time.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a storage system that stores data thatis employed by a computer and that receives updating of data from acomputer, and in particular relates to processing for maintaining copiesof data between a plurality of storage systems.

2. Description of the Related Art

In Laid-open European Patent Application No. 0672985, a technique isdisclosed whereby the data that is employed by a computer is stored by astorage system and a copy of this data is stored in a separate storagesystem arranged at a remote location, while reflecting the writesequence of the data. In the processing indicated in Laid-open EuropeanPatent Application No. 0672985, the source storage system that hasreceived the write data from the primary host computer reportscompletion of reception of the write data to the primary host computeronly after reception of the write data. After this, the primary hostcomputer reads a copy of the write data from the source storage system.A write time, which is the time at which the write request in respect ofthe write data was issued, is applied to this write data and, when thewrite data is read by the primary host computer, the write time is alsotransferred to the primary host computer. In addition, the primary hostcomputer transfers the write data and the write time to the secondaryhost computer. After receiving the write data and the write time, thesecondary host computer writes information including the write time to acontrol volume in the storage system on the secondary side and, inaddition, writes the write data in the target storage system in thewrite time sequence, with reference to the write times at which thevarious items of write data were presented. By writing the write data inthe target storage system in the write time sequence, it is possible tomaintain consistent data in the target storage system.

If write data were to be reflected to the target storage systemneglecting the write sequence (the operation of storing write data inthe target storage system will hereinbelow be referred to as“reflecting” the data), for example in the case of a bank accountdatabase, in processing to transfer funds from an account A to anaccount B, it would not be possible to reproduce the debiting of theaccount A and the crediting of the account B as a single transaction andit would be possible for example for a period to occur in the targetstorage system in which the balance of the account B was credited beforedebiting of the balance of the account A. If, in this case, some faultoccurred in the source storage system rendering it unusable prior todebiting the balance of the account A in the target storage system,mismatching data would be left in the target storage system, with theresult that incorrect processing would be performed if business were tobe subsequently continued using the secondary host computer.Consequently, by storing the write data in the target storage systempreserving the write sequence, consistent data can be maintained, makingit possible to guarantee correctness of a sequence of related operationsin respect of related data.

U.S. Pat. No. 6,092,066 discloses a technique whereby the data that isused by a computer is stored in a storage system and, by copying thedata that is stored in this storage system to a separate storage systemarranged at a remote location, the data can be maintained in theseparate storage system even if the first storage system has becomeunusable due to for example a natural disaster or fire.

U.S. Pat. No. 6,209,002 discloses a technique whereby data employed by acomputer is stored in a storage system and, by copying the data that isstored in this storage system to a separate storage system arranged at aremote location, and additionally copying the data that has beenreceived by this separate storage system to a third storage system, ahigh level of redundancy can be obtained in respect of data.

SUMMARY OF THE INVENTION

In the technique that is disclosed in Laid-open European PatentApplication No. 0672985, consistency of the copy of data stored in thetarget storage system cannot be maintained unless the host computerapplies a write time to the write data, since the write sequence ismaintained using the write time applied to the write data by the hostcomputer when the write data from the host computer is reflected to thetarget storage system. In the case of a so-called mainframe hostcomputer, the write time is applied to the write request, but, in thecase of a so-called open system host computer, the write time is notapplied to the write request. Consequently, in the technique disclosedin Laid-open European Patent Application No. 0672985, consistency of thecopy of the data stored in the target storage system with I/O from anopen system host computer cannot be maintained.

Also in the case of U.S. Pat. No. 6,092,066 and U.S. Pat. No. 6,209,002,there is no disclosure concerning maintenance of consistency of a copyof data stored in a target storage system when the host computersinclude an open system host computer.

Accordingly, in a computer system in which data that is employed bycomputer is stored in a storage system and the data that is stored inthis storage system is transferred to a separate storage system so thata copy of the data is also held in this separate storage system, thereis herein disclosed a technique for maintaining consistency of the copyof the data stored in the separate storage system (i.e. the targetstorage system) even in respect of data written to the storage system bya host computer that does not apply a write time to the write data, suchas an open system host computer.

The system comprises a first storage device system having a firstlogical volume coupled to a computer and in which data received from thecomputer is stored and a second storage device system coupled to thefirst storage device system and having a second logical volume in whicha copy of data stored in the first logical volume is stored.

The first storage device system applies time information to the writedata received from the computer and sends the write data and this timeinformation to the second storage device system; the second storagedevice system stores the write data received from the first storagedevice system in the second logical volume in accordance with the timeinformation applied to this write data.

In a computer system in which data that is employed by computer isstored in a storage system and the data that is stored in this storagesystem is transferred to a separate storage system so that a copy of thedata is also held in this separate storage system, it is therebypossible to maintain consistency of the copy of the data that is storedin the separate storage system (target storage system), even in the caseof data stored in the storage system by a host computer that does notapply the write time to the write data, such as an open system hostcomputer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of the layout of a computer systemaccording to embodiment 1;

FIG. 2 is a diagram showing an example of a logical volume group;

FIG. 3 is a flow diagram showing an example of processing in the casewhere a write request is received by a storage device A;

FIG. 4 is a view showing an example of group management information;

FIG. 5 is a view showing an example of write data management informationfor managing write data;

FIG. 6 is a flow diagram showing an example of transfer processing ofwrite data from the storage device A to a storage device B;.

FIG. 7 is a view showing an example of remote logical volume informationof a logical volume;

FIG. 8 is a view showing an example of arrived write time information;

FIG. 9 is a flow diagram showing an example of reflection processing ofwrite data in the storage device B;

FIG. 10 is a flow diagram showing another example of processing in thecase where the storage device A has received a write request;

FIG. 11 is a flow diagram showing another example of processing in thecase where the storage device A has received a write request;

FIG. 12 is a view showing an example of the layout of a computer systemaccording to embodiment 2;

FIG. 13 is a view showing an example of the layout of a computer systemaccording to embodiment 3;

FIG. 14 is a flow diagram showing another example of processing in thecase where the storage device A in embodiment 3 has received a writerequest;

FIG. 15 is a flow diagram showing an example of processing in the casewhere the management software A gives, instructions for deferringprocessing of a write request in respect of the storage device A andcreation of a marker;

FIG. 16 is a view showing an example of marker number information;

FIG. 17 is a view showing another example of write data managementinformation;

FIG. 18 is a flow diagram showing an example of transfer processing ofwrite data from the storage device A in embodiment 3 to the storagedevice B;

FIG. 19 is a flow diagram showing an example of reflection processing ofwrite data in the storage device B in embodiment 3;

FIG. 20 is a flow diagram showing another example of reflectionprocessing of write data in the storage device B in embodiment 3; and

FIG. 21 is a view showing an example of the layout of a computer systemaccording to embodiment 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below. However, itshould be noted that the present invention is not restricted to theembodiments described below.

Embodiment 1

FIG. 1 is a view showing an example of the layout of a computer systemaccording to a first embodiment.

This system comprises a storage device (also referred to as a storagesystem) A100, a mainframe host computer A (also called MFA) 600, an opensystem host computer A700, a storage device B190, a mainframe hostcomputer B (also referred to as MFB) 690 and an open system hostcomputer B790. The storage devices A 100 and MFA 600 and the open systemhost A 700 are respectively connected by I/O paths 900. The storagedevice B 190 and MFB 690 and open system host B 790 are alsorespectively connected by I/O paths 900. The MFB 690 and open systemhost B 790 are normally a standby system. The MFA 600, MFB 690 and opensystem host A 700 and open system host B 790 are connected by a network920.

The MFA 600 and MFB 690 include an OS 610 and application software (APP)620. Also, the open system host A 700 and open system host B 790likewise include an OS 710 and APP 720. An I/O request issued from theAPP of the MFA 600, MFB 690, open system host A 700, or open system hostB 790 through the OS is issued to the storage device A 100 or storagedevice B 190 through the I/O path 900. In this case, software such as aDBMS is included in the APP 620 or APP 720.

The storage device A 100 comprises a control section 200, control memory300 and cache 400. The control section 200 comprises a write datareception section A 210 and write data transfer section A 220. Thecontrol section 200 accesses the control memory 300 and performs thefollowing processing, utilizing the information stored in the controlmemory 300. The cache 400 comprises high-speed memory that chieflystores the read data or write data so that the storage device A canachieve a high I/O processing performance by employing the cache 400. Itshould be noted that, preferably, these components are duplicated andprovided with back-up power sources, for purposes of fault resistanceand availability.

The storage device B 190 also comprises a control section 200, controlmemory 300 and cache 400. The control section 200 comprises a write datareception section B 211 and write data reflection instruction section230 and write data reflection section 240. The role of the controlmemory 300 and cache 400 is the same as in the description of thestorage device A 100 above.

The storage device A 100 and storage device B 190 provide logicalvolumes 500 constituting data storage regions in respect of the MFA 600,open system host A 700, MFB 690 and open system host B 790. It is notnecessary that a single logical volume 500 should constitute the singlephysical device; for example it could be constituted by a set of storageregions dispersed on a plurality of magnetic disc devices. Also, alogical volume may have for example a mirror construction or aconstruction that has redundancy such as for example a RAIDconstruction, in which parity data is added.

The storage device A 100 provides a logical volume 500 as describedabove; however, in the case of the MFA 600 and open system host A 700,the type of logical volume 500 that is provided is different from thatprovided in the case of the storage device A 100; also, the logicaland/or physical interfaces of the I/O paths 900 are different. The sameapplies to the storage device B 190, MFB 690 and open system host B 790.The time of the write request 630 is included in the write request 630from the MFA 600 as the write time 650, but is not included in the writerequest 730 from the open system host A 700.

The storage device A 100 and the storage device B 190 are connected bytransfer paths 910. As will be described, the storage device A 100 andthe storage device B 190 can hold a copy of the content of one logicalvolume in another logical volume. In this embodiment, a copy of thecontent of the logical volume 500 of the storage device A 100 is held inthe logical volume 500 of the storage device B 190; the content of theupdating performed on the logical volume 500 of the storage device A 100is also stored in the logical volume 500 of the storage device B 190 bybeing sent to the storage device B 190 through the transfer path 910. Aswill be described, the storage device A 100 and the storage device B 200hold management information regarding the copy, indicating therelationship between the logical volumes and maintenance of the copyreferred to above is performed by using this management information. Therelationship between the logical volumes and the relationship of thelogical volume groups, to be described, is set by the user in accordancewith the user's needs.

In this embodiment, the relationships between the logical volumes aregrouped. FIG. 2 is a diagram showing an example of a group of logicalvolumes. The broken lines indicate the copy relationship between thelogical volumes 500 or between the logical volume groups i.e. thecorrespondence relationship of the source and target. In thisembodiment, the sequence of write data in the storage device A 100 andreflection in the storage device B 190 are managed in units of logicalvolume groups comprising a plurality of such logical volumes andallocation of the necessary resources for processing as described aboveis also performed in units of logical volume groups.

If these are performed for each of the individual logical volumes, thelarge number of items to be managed makes the management processcomplicated and there is also a possibility of the resources requiredfor this processing being increased, due to the large number of items tobe processed. On the other hand, if the entire storage device A 100 istreated as a unit, detailed management can no longer be performed. Inparticular, since demands such as performance in regard to the logicalvolumes 500 differ greatly between a mainframe host and an open systemhost, it is desirable to arrange for example for manual controloperations from the user in regard to processing and setting such as oftuning conditions to be accepted separately, by arranging for such hoststo perform processing separately, divided into respective groups. Bysetting up logical volume groups in this way, flexible copy processingmanagement can be provided in response to the requirements of users orbusinesses.

Next, processing of writing of data onto each logical volume 500,transfer of data to a storage device B 190 and processing for reflectionof data in the storage device B 190 will be described for the case wherethe logical volumes 500 that are used by the MFA 600 and the open systemhost A 700 are arranged to belong to different logical volume groups. Bymeans of these processes, reflection to a copy is performed in writesequence between the various logical volumes of the storage device A 100and, regarding consistency between copies, it is arranged that mutualconsistency can always be maintained between the mainframe host data andopen system host data.

FIG. 3 is a view showing the processing that is performed in the casewhere a write request is received from the MFA 600 or open system host A700 in respect of a logical volume 500 (logical volume 500 constitutingthe source) where a copy of the logical volume 500 is being created. Thewrite data reception section A 210 receives a write request from the MFA600 or open system host A 700 (step 1000). If the write time 650 isincluded in the write request that is received (step 1001), the writedata reception section A 210 stores the write data in the cache 400(step 1002) and creates (step 1003) write data management information330 by applying (assigning) a sequential number to the write data. Thewrite data reception section A 210 then records the write time 650 inthe write data management information 330. Also, when the sequentialnumber is applied, the write data reception section A 210 obtains thesequential number from the group management information 310 of thelogical volume group to which the logical volume that is being writtenbelongs and records a value obtained by adding 1 thereto in the writedata management information 330 as the sequential number of the writedata, and records this new sequential number in the group managementinformation 310.

FIG. 4 is a view showing an example of group management information 310of the various logical volume groups. The group ID is the ID foridentifying a logical volume group in the storage device A 100. Thesequential numbers are numbers that are continuously given to write datain respect of a logical volume belonging to the logical volume group inquestion. Numbers successively increased by 1 in each case are appliedto such write data, the initial value being for example 0. The logicalvolume number is the number of the logical volume that belongs to thelogical volume group in question. The logical volume number is the ID ofthe logical volume belonging to the logical volume group in question inthe storage device A 100. The remote storage device ID has a logicalvolume group that is paired with the logical volume group in questionand is an ID (e.g. serial number) that specifies the storage device (inthis embodiment, the storage device B 190) where a copy of the contentof the logical volume belonging to the logical volume group in questionis stored. The remote group ID is an ID that specifies the logicalvolume group that is paired with the logical volume group in question inthe remote storage device (storage device B 190) i.e. the logical volumegroup to which the logical volume 500 (also called the remote logicalvolume) belongs in which a copy of the content of the logical volumebelonging to the logical volume group in question is stored.

FIG. 5 is a view showing an example of write data management information330 for managing the various write data. The logical volume ID is the IDof the logical volume in which the write data is stored. The writeaddress is the write start address of the write data in question in theaforesaid logical volume. The write data length is the length of thewrite data in question. The write data pointer is the storage startaddress of the write data in question in the cache 400. The sequentialnumbers are numbers that are continuously given to write data in thelogical volume group and to which the logical volume belongs in whichthe write data is written. The write time will be discussed below. The“transfer required” bit is a bit that indicates whether or not the writedata in question needs to be transferred to the storage device B and isset to ON when write data management information 330 is created byreceipt of write data by the write data reception section A 210. Thewrite data management information 330 is managed in the form of a listfor example for each logical volume group.

Returning to FIG. 3, in step 1004, the write data reception section A210 records the write time 650 as the write time information 340 in thecontrol memory 300.

If, in step 1001, no write time is included in the write request, thewrite data reception section A 210 stores the write data in the cache400 (step 1005) and obtains from the write time information 340 a writetime, which it applies (assigns) to the write data, and creates writedata management information 330 (step 1006) by applying a sequentialnumber obtained from the group management information 310. At this time,the write data reception section A 210 then records the time at whichthe write time information 340 was recorded, as the write time of thewrite data management information 300, and finds a sequential number bythe same procedure as in the case of step 1003 described above andrecords this sequential number in the write data management information300.

Finally, in step 1007, completion of writing is reported to the MFA 600or to the open system host A 700. The aforesaid processing does notinclude the time-consuming processing of physically writing the writedata that is stored in the cache 400 to the recording medium of thelogical volume 500 or of transferring the write data to the storagedevice B 190; this processing is performed subsequently in asynchronousfashion, with an appropriate timing. Consequently, the time requireduntil reporting of completion of writing after receiving the writerequest by the write data reception section A 210 need only be a shorttime, so rapid response to the MFA 600 or open system host A 700 can beachieved.

FIG. 6 is a view showing an example of transfer processing of write datato the storage device B 190 from the storage device A 100. The writedata transfer section A 220 finds (step 1100) the information relatingto the write data that is transferred to the storage device B 190 byreferring to the list of the write data management information 330 tofind the write data that needs to be transferred and, in addition,referring to the write data management information 330, group managementinformation 310 and remote logical volume information 320. Thisinformation includes the write address acquired from the write datamanagement information 330, the write data length, the sequentialnumber, the write time, the remote storage device ID acquired from theremote logical volume information 320, the remote logical volume number,and the remote group number obtained from the group managementinformation 310 using the logical volume ID.

FIG. 7 is a view showing an example of the remote logical volumeinformation 320 of the various logical volumes. The logical volume ID isthe ID of the logical volume on the source side (logical volume 500included in the storage device A 100 in embodiment 1). The remotestorage device ID is an ID (for example a serial number) specifying thestorage device (storage device B 190 in embodiment 1) having the logicalvolume (also called the remote logical volume) in which is stored a copyof the data stored by the logical volume in question that is paired withthe logical volume in question. The remote logical volume ID is an IDthat specifies the remote logical volume (i.e. the logical volume 500 onthe target side, where a copy of the data that was stored in the logicalvolume is stored) in the remote storage device (storage device B 190 inembodiment 1).

Next, returning to FIG. 6, the write data transfer section A 220transfers (step 1101) to the storage device B 190 the write data and theinformation found in step 1100. The write data reception section B 211of the storage device B stores (step 1102) the received write data andinformation in the cache 400 and creates (step 1103) write datamanagement information 330 from the received information. The items ofthe write data management information 330 of the storage device B 190are the same as the items of the write data management information 330of the storage device A 100. The content of the write data managementinformation 330 of the storage device B 190 differs from that of thewrite data management information 330 of the storage device A 100 inthat the logical volume ID is the ID of the logical volume 500 on thetarget side where the copy is stored and the write data pointer is thestorage start address of the write data in the cache 400 of the storagedevice B 190 and the “transfer needed” bit is normally OFF, but isotherwise the same.

The storage device B 190 also has group management information 310, butthe items thereof are the same as in the case of the storage device A100. Regarding the content of the group management information 310, thegroup ID is an ID that specifies the logical volume group to which thelogical volume 500 on the side of the target where the copy is storedbelongs, the remote storage device ID is the ID of the storage device(storage device A 100 in the case of embodiment 1) constituting thesource and the remote group ID is an ID that specifies the logicalvolume group to which the remote logical volume (i.e. the logical volume500 constituting the source) belongs in the remote storage device(storage device A 100 in embodiment 1). The storage device B 190 alsohas remote logical volume information 320, but the items thereof are thesame as in the case of the storage device A 100 and, regarding itscontent, the logical volume ID is an ID that specifies the logicalvolume 500 where the copy is stored, the remote storage device ID is anID that specifies the ID of the storage device (storage device A 100)constituting the source and the remote logical volume ID is an ID thatspecifies the remote logical volume (logical volume 500 constituting thesource) in the remote storage device (storage device A 100).

Returning to FIG. 6, next, the write data reception section B 211updates the arrived write time information 350 (step 1104).

FIG. 8 is a view showing an example of arrived write time information350 of the various groups. The group ID is an ID that specifies thelogical volume group in the storage device B 190. The latest write timeof the arrived write data is the latest-time closest to the currenttime, of the write times applied to the write data received by the writedata reception section of B 211, in respect of the logical volume groupsof the storage device B 190. However, if it appears, from the sequentialnumber order, that some of the write data has not yet arrived (some ofthe sequence of write data is missing), the latest time of the writetime applied to these items of write data is recorded as the arrivedwrite data time information, taking the continuous time comparison rangein the order of the sequential numbers as being up to the final writedata (write data immediately preceding the missing data).

In transfer of the write data between the write data transfer section A220 and the write data reception section B 211, a plurality of items ofwrite data may be simultaneously transferred in parallel. The write datais therefore not necessarily received in the write data receptionsection B 211 in the order of the sequential numbers but, as will bedescribed, the write data is reflected in the order of the sequentialnumbers to each of the logical volume groups (i.e. it is stored in thelogical volumes of the storage device B 190), so the write data isreflected to the copy in the order of updating (i.e. in the order ofwriting of the write data in the storage device A 100).

Returning once more to FIG. 6, finally, the write data reception sectionB 211 reports completion of reception of the write data to the writedata transfer section A 220 (step 1105). The write data transfer sectionA 220 of the storage device A 100 that has received this write dataturns the “transfer required” bit of the write data managementinformation 330 OFF in respect of the write data corresponding to thereport of completion of reception of write data. At this time, thestorage device A 100 may discard from the cache the arrived write datathat was held for transfer to the storage device B 190.

FIG. 9 it is a view showing an example of the reflection processing ofwrite data in the storage device B 190 (i.e. the processing of storageof the write data to the logical volume).

The write data reflection instruction section B 230 checks the arrivedwrite time information 350 of all the logical volume groups of thestorage device B 190 and finds, of these, the earliest time (step 1200).The write data reflection instruction section B 230 gives instructions(or permission) (step 1201) to the write data reflection section B 240for reflection to these logical volumes of the write data whose writetime is previous to the time that was thus found. When the write datareflection section 240 receives these instructions (or permission), byreferring to the write data management information 330 and groupmanagement information 310, it reflects the write data in the designatedtime range (i.e. the write data whose write time is previous to the timefound in step 1200), in the order of the write times, or, if these writetimes are the same, in the order of the sequential numbers in thevarious logical volume groups, in respect of the logical volume 500 inwhich the copy is stored (i.e. the write data is stored in the logicalvolume on the target side) (step 1202). After completion of reflectionof all of the write data in the range specified in step 1202, the writedata reflection section B 240 reports completion of the instructedprocessing (step 1203) to the write data reflection instruction section230. The storage device B may discard the reflected write data from thecache 400.

By means of the above processing from step 1200 to step 1203, one ofcycle of reflection processing is completed. The write data reflectioninstruction section B 230 and the write data reflection section B 240repeat the above cycle in order to reflect the write data transferredfrom the storage device A continuously.

By means of the above processing, a copy of the updated *data of thestorage device B 190 is stored maintaining the order between updating ofdata by the mainframe host and updating of data by the open system host.Regarding data consistency between the copies, mutual consistency can bemaintained between the data of the mainframe host and the data of theopen system host.

Specifically, the storage device A 100 utilizes the write time 650contained in the write request 630 received from the mainframe host andapplies a write time also to the write data received from the opensystem host and, furthermore, manages the received write data using boththe write times and the sequential numbers. The target storage device B190 designates the write data that is capable of being reflected (i.e.that is capable of storage in a logical volume on the target side) usingthe sequential numbers and the write times and stores the designatedwrite data in a logical volume on the target side. As a result, even ifbuffering and/or transferring are provided in parallel mid-way, writeorder is maintained between the data written from the mainframe host andthe data written from the open system host, so copy data can be storedin a logical volume of the storage device B 190 on the target side.

Also, even if some fault occurs in for example the storage device A 100,so that previously updated write data does not reach the storage deviceB 190, since the sequential numbers will not be continuous in respect ofthe write data of write times subsequent to the write time of the writedata that failed to arrive, reflection thereof will not be allowed. Gapsof updating of data cannot therefore occur in the target side storagedevice B 190 and consistency between the source storage device A 100 andtarget storage device B 190 is ensured. As a result, even if a faultoccurs in the source storage device A 100, business can be continuedusing the content of the logical volume 500 of the storage device B 190,which is matched with the MFB 690 and/or open system host B 790.

Also, since, in the above processing, write times are applied to all ofthe write data received by the storage device A 100, irrespective ofwhether the host that employs the data is a mainframe host or opensystem host, it is possible to ascertain information such as up to whichwrite time the write data in any desired logical volume 500 has beentransferred from the storage device A 100 to the storage device B 190 orhas arrived at the storage device B 190 or has been reflected at thestorage device B 190 (i.e. has been stored in a logical volume).

It should be noted that, in order to lighten the processing load in theabove step 1202, the write data in the designated time range may bestored in the logical volume 500 that stores the copy in sequentialnumber order in the various logical volume groups, neglecting the writetime order. In this case, consistency between the copies (i.e. betweenthe logical volumes of the storage device B 190 on the target side) ismaintained by the timing of the reports of completion of processing instep 1203. If it is desired to hold consistent data of the periodbetween a report of completion of processing and the next report ofcompletion of processing, a snapshot of the logical volume 500 in whichthe copy is stored may be acquired with the timing of the report ofcompletion of processing. The technique disclosed in for example U.S.Pat. No. 6,658,434 may be employed as a method of acquiring such asnapshot. In this method, the storage content of a logical volume 500(source volume) in which is stored the data whereof a snapshot is to beacquired is copied to another logical volume 500 (target volume) of thestorage device B 190, so that the updated content is reflected also tothe target volume when the source of volume is updated. However, in thisembodiment, once the snapshot of the source volume has been stored inthe target volume, the content of the target volume is frozen andverified by stopping reflection at that time.

Also in the transfer processing of the above write data, it was assumedthat, initially, the write data transfer section A 220 transfers thewrite data in respect of the write data reception section B 211;however, it would be possible for the write data reception section B 211to initially issue a write data transfer request in respect of the writedata transfer section 220 and for the write data transfer section A 220to transfer the write data in respect of the write data receptionsection B 211 after having received this request. By employing writedata transfer requests, the pace of transfer of write data can beadjusted in accordance with for example the processing condition or loadof the storage device B 190 or the amount of write data that has beenaccumulated.

Also, in the above processing, it was assumed that the location ofstorage of the write data was the cache 400; however, by preparing aseparate logical volume 500 for write data storage, the write data couldbe stored in this logical volume 500. In general, a logical volume 500of large volume may be prepared in respect of the cache 400, so thismakes it possible for more write data to be accumulated.

Also, in the above processing, it was assumed that the write timeinformation 340 was updated by the write time 650 of reception from themainframe host; however, it may be arranged for the storage device A 100to possess an internal clock and to constantly update the write timeinformation 340 by reference to this clock. In this case, FIG. 10 showsan example of the processing that is executed when a write request inrespect of a logical volume 500 (logical volume 500 constituting thesource) where the storage device A 100 creates a copy is received fromthe MFA 600 or open system host A 700. This processing is processingcorresponding to the processing shown in FIG. 3.

The write data reception section A 210 receives (step 1300) a writerequest from the MFA 600 or open system host A 700. The write datareception section A 210 stores (step 1301) the write data in the cache400 and applies a write time to the write data by referring to the writetime information 340 that is constantly updated in accordance with theclock provided in the storage device A 100, and creates (step 1302)write data management information 330 by applying a sequential number tothe write data, by referring to the group management information 310.Finally, completion of writing is reported to the MFA 600 or open systemhost A 700 (step 1303).

Also, in the above processing, a time is used in the write timeinformation 340 or the write time of the write data managementinformation 300 or the arrived write time information 350; however, thetime that is employed for this purpose need not necessarily be of theform of years, months, days, hours, minutes, seconds, milliseconds,microseconds, nanoseconds or a total of an ordinary time and instead asequential number could be employed. In particular, FIG. 11 shows anexample of the processing when the storage device A 100 has received awrite request in respect of the logical volume 500 (logical volume 500constituting the source), where the copy is created, from the MFA 600 oropen system host A 700, in a case where the storage device A 100 itselfupdates the write time information 340. This processing is processingcorresponding to FIG. 3 or FIG. 10. It should be noted that, in FIG. 11,the initial value of the write time information 340 may for example be 0and numbers successively incremented by 1 may be applied to the writedata as shown below as the write times.

The write data reception section A 210 receives a write request (step1400) from the MFA 600 or open system host A 700. The write datareception section A 210 stores the write data in the cache 400 (step1401), reads the number from the write time information 340 and appliesto the write data (step 1402) as the write time the value obtained byincrementing this by 1. Then the write data reception section A 210records the value after incrementing by 1 as the write time information340, thereby updating the write time information 340 (step 1403). Thewrite data reception section A 210 also creates the write datamanagement information 330 (step 1405) by applying a sequential numberto the write data (step 1404) by referring to the group managementinformation 310. The write data reception section A 210 finally reportscompletion of writing (step 1406) to the MFA 600 or open system host A700.

When a sequential number is employed as the write time in this manner,in the storage device B 190, instead of the write data reception sectionB 211 being arranged to update the arrived write time information 350using the write time applied to the write data received and the writedata reflection instruction section B 230 being arranged to designatethe range of write data capable being stored in a logical volume of thestorage device B by checking the arrived write time information 350 ofthe various logical volume groups, it may be arranged for the write datareflection section 240 to reflect (i.e. store) the write data arrivingat the storage device B by referring to the sequential number recordedat the write time of the write data management information 330 in thelogical volume 500 without skipping numbers in the number sequence.

Embodiment 2

FIG. 12 is a view showing an example of the layout of a computer systemaccording to a second embodiment.

The differences with respect to embodiment 1 lie in that the MFA 600 andopen system host A 700 are connected with the storage device C 180through an I/O path 900 and the storage device C 180 is connected withthe storage device A 100 through a transfer path 910. In thisembodiment, a copy of the data stored in the logical volume 500 of thestorage device C 180 is stored in a logical volume 500 of the storagedevice A 100. Further, a copy of the data stored in the logical volume500 of the storage device A is stored in the logical volume 500 of thestorage device B 190 in processing like the processing described inembodiment 1. That is, in this embodiment, a copy of the data stored inthe logical volume 500 of the storage device C 180 is stored in thestorage device A 100 and the storage device B 190. In order to implementsuch processing, the storage device C 180 is provided with the variousitems of information and a construction like that of the storage deviceA 100 described in embodiment 1.

When the storage device C 180 has received a write request 630 or awrite request 730 for the logical volume 500 from the MFA 600 or opensystem host A 700, it stores the received write data 640 or write data740 in a logical volume in the storage device C 180 and transfers thisto the write data reception section A 210 of the storage device A 100.At this point, in contrast to the processing described in embodiment 1,the storage device C 180 sends notification of completion of writing tothe MFA 600 or open system host A 700 after waiting for notification ofcompletion of reception from the write data reception section A 210, andthe storage device C 180 is thereby able to guarantee that a copy of thewrite data 640 or write data 740 that was written thereto is present inthe storage device A 100. In this way, if for example due to theoccurrence of some fault in the storage device C 180 or on thetransmission path 910, transfer of data to the storage device A 100 hasnot succeeded, the MFA 600 or open system host A 700 will not deem writedata that have not been transferred to the storage device A 100 to havebeen written but will only deem write data that have been received bythe storage device A 100 to have actually been written; a copy asexpected by the APP 620 on the MFA 600 or the APP 720 on the open systemhost A 700 will therefore exist on the storage device A 100.Furthermore, after all of the write data received by the storage deviceA 100 have been sent to the storage device B 190, a copy as expectedwill also exist on the storage device B 190, so, at the time where theprocessing executed by the MFA 600 or open system host A 700 wasinterrupted, the MFB 690 or open system host B 790 will be able tocontinue business using data as expected identical with the data thatare recognized as having been written by the MFA 600 or open system hostA 700.

As initially indicated in embodiment 1, when the write time information340 is updated by the write time 650 applied to the write data, thewrite data reception section C 212 of the storage device C 100, if awrite time 650 is included in the received write request 630, recordsthe write time also in the write data management information 330 and thewrite data transfer section C 222 also transfers this write time to thewrite data reception section A210 of the storage device A 100 whenperforming write data transfer. After receiving the write data and thewrite time, the write data reception section A 210 processes the writedata and the write time received from the storage device C 180 by thesame method as the processing of the write request 630 that was receivedfrom the mainframe host in embodiment 1; consistency between the copiesstored in the logical volumes in the storage device A 100 is therebymaintained and consistency between the write data issued from themainframe host and the write data issued from the open system host canthereby be maintained.

In this way, even if, due for example to a large-scale disaster, faultsoccur in both of the storage device C 180 and the storage device A 100,business can be continued using the consistent content of the logicalvolume 500 of the storage device B 190, which was matched with the MFB690 and open system host B 790. As indicated in the final part ofembodiment 1, when the write time information 340 is updated from thestorage device A 100 itself, transfer of the write time from the storagedevice C 180 is unnecessary, so that, after receiving the write datafrom the storage device C 180, the write data reception section A 210may perform processing on the write data like the processing of FIG. 11indicated in the latter part of embodiment 1.

It should be noted that there may be a plurality of storage devices C180 that connect to the storage device A 100.

Also, although not shown, if the mainframe host and open system host areconnected by an I/O path with the storage device A 100, the mainframehost or open system host that is connected with the storage device A maycontinue the business that was being conducted by the MFA 600 or opensystem host A 700 using the consistent content of a logical volume 500of the storage device A 100 that was matched therewith, in the eventthat a fault occurs in the MFA 600 or open system host A 700 or storagedevice C 180.

Embodiment 3

FIG. 13 is a view showing an example of the construction of a computersystem according to Embodiment 3.

The chief differences with respect to embodiment 1 lie in that there area plurality of respective storage devices A 100 and storage devices B190, the MFA 600 and open system host A 700 are connected through an I/Opath 900 respectively with a plurality of storage devices A 100, the MFB690 and the open system host B 790 are connected through an I/O path 900respectively with a plurality of storage devices B 190, the MFA 600includes management software A 800 and the MFB 690 includes managementsoftware B 890. Other differences will be described below.

Hereinbelow, the processing in respect of writing performed to thevarious logical volumes 500, transfer of write data to the storagedevice B 190 and the processing of reflection of write data in thestorage device B 190 (i.e. storage of the write data in the logicalvolume) will be described in respect of the logical volumes 500 employedby the MFA 600 and the open system host A 700. This processing ensuresthat mutual consistency is maintained between the data of the mainframehost and the data of the open system host in regard to consistencybetween copies respectively stored in the plurality of logical volumesthat are possessed by the plurality of storage devices B 190.

FIG. 14 is a view showing an example of the processing when a writerequest in respect of the logical volume 500 (logical volume 500constituting the source) in which a copy is created by the storagedevice A 100 is received from the MFA 600 or open system host A 700.

The write data reception section A 210 receives (step 1500) a writerequest from the MFA 600 or open system host A 700. The write datareception section A 210 stores the write data in the cache 400 (step1501) or, as in embodiment 1, creates write data management information330 (step 1502) by acquiring a sequential number by referring to thegroup management information 310. Finally, the write data receptionsection A 210 reports to the MFA 600 or open system host A 700completion of writing (step 1503). The group management information 310is the same as that in the case of embodiment 1. The write datamanagement information 330 of this embodiment will be described later.

FIG. 15 is a view showing an example of the processing when themanagement software A 800 gives instructions for deferment of processingof write requests in respect of the storage device A 100 and creation ofa marker. As will be described later, consistency is established betweenthe copies stored in the plurality of storage devices B 190 bysubsequently performing synchronization of reflection to the copies,with the timing with which this processing was performed during updatingof the logical volume 500 of the storage device A 100.

First of all, the management software A 800 gives instructions fordeferment of processing of write requests to all of the storage devicesA 100 (step 1600). On receipt of these instructions, the write datareception section A 210 defers processing of write requests (step 1601)and reports to the management software A 800 the fact that deferment hasbeen commenced (step 1602). After the management software A 800 hasconfirmed that commencement of deferment has been reported from all ofthe storage devices A 100 that have been so instructed, processingadvances to the following processing (step 1603 and step 1604).

Next, the management software 800 instructs all of the storage devices A100 to create markers (step 1605). This instruction includes a markernumber as a parameter. The marker number will be described subsequently.On receipt of this instruction, the marker creation section A 250records the received marker number in the marker number information 360shown in FIG. 16 stored in the control memory 300 (step 1606) andcreates (step 1607) special write data (hereinbelow called a marker) forinformation transmission in respect of all of the logical volume groups.A marker is write data in which a marker attribute is set in the writedata management information 300.

FIG. 17 is a view showing an example of write data managementinformation 330 of write data in this embodiment: a marker attribute bitand marker number are added to the write data management information 330of embodiment 1.

The marker attribute bit is a bit indicating that the write data inquestion is a marker and is OFF in the case of ordinary write data butis set to ON in the case of a marker. A marker number as described aboveis set in the “marker number”. The sequential number in the group isacquired and applied in respect of a marker in the same way as in thecase of ordinary write data. Specifically, in marker creation, themarker creation section A 250 obtains a sequential number from the groupmanagement information 310 of the group in the same way as in theprocessing of the write data reception section A 210 and records a valueobtained by adding 1 thereto in the write data management information330 as the sequential number of the aforesaid marker, and records thenew sequential number in the group management information 310. When thesequential number has been applied in this way to the marker, it istransferred to the storage device B 190 in the same way as in the caseof ordinary write data, but the marker is not reflected to the logicalvolume 500.

The marker number is a number for identifying the instruction inresponse to which the marker was created; when a marker creationinstruction is issued by the management software A 800, for example theinitial value thereof is 0 and the marker number is incremented by 1before being issued. The management software A 800 may confirm thecurrent marker number by reading the marker number recorded in themarker number information 360.

Returning to FIG. 15, after the marker creation section A 250 hascreated a marker in respect of all of the logical volume groups, themarker creation section A 250 reports completion of marker creation tothe management software A 800 (step 1608). After confirming thatcompletion of marker creation has been reported from all of thedesignated storage devices A 100, the management software A 800 proceedsto the subsequent processing (step 1609, step 1610).

The management software A 800 gives instructions (step 1611) forcancellation of deferment of processing of write requests to all of thestorage devices A 100. On receipt of these instructions, the write datareception section A 210 cancels deferment of processing of writerequests (step 1612) and reports to the management software A 800 (step1613) the fact that such deferment has been cancelled.

FIG. 18 is a view showing an example of transfer processing of writedata to a storage device B 190 from a storage device A 100. Thisprocessing is substantially the same as the transfer processingdescribed in FIG. 6 of embodiment 1, but differs in that no updating ofthe arrived write time information 350 is performed by the write datareception section B 211. It should be noted that the write datamanagement information 330 of the storage device B 190 is the same asthe write data management information shown in FIG. 17, described above;in step 1703, the presence or absence of the marker attribute of thewrite data and/or the marker number recorded in the write datamanagement information 330.

FIG. 19 is a view showing an example of the processing of reflection(storage) of write data to a logical volume in the storage device B 190.First of all, the management software B 890 gives instructions forreflection of the write data, as far as the marker, to the logicalvolume 500 in which a copy is stored (step 1800) to all of the storagedevices B 190. After receiving such an instruction, the write datareflection section B 240 refers to the write data information 330 andgroup management information 310 and reflects (step 1801) the write dataas far as the marker, in the sequential number order in each group, tothe logical volume 500 in which the copy is stored. Specifically, thewrite data reflection section B 240 continues to store the write data inthe logical volume in the order of the sequential numbers, but stopsdata storage processing on finding write data with the marker attribute(i.e. a marker) and then reports completion of reflection to themanagement software B 890 (step 1802). In the aforementioned processing,the write data reflection section B 240 checks the marker numbers of themarkers that are recorded in the write data management information 330and thereby ascertains whether the marker number is correct (whether themarker conforms to rules which are the same as the marker numberdecision rules, described above, for example of being a number whoseinitial value is 0 and that is incremented by 1 with respect to theprevious marker number). If the marker number is not correct, the writedata reflection section B 240 reports an abnormal situation to themanagement software B 890; if the marker number is correct, the writedata reflection section B 240 records the marker number in the markernumber information 360 and reports a normal situation. The managementsoftware B 890 may confirm the current marker number by reading themarker number that is recorded in the marker number information 360.

After confirming that a “normal reflection completed” report has beenobtained from all of the storage devices B 190 that had been designated,the management software B 890 proceeds to the next processing (step1803, step 1804).

Next, the management software B 890 gives instructions (step 1805) forupdating of the snapshot of the logical volume 500 that stores the copyto all of the storage devices B 190. After receiving this instruction,the snapshot acquisition section B 260 updates (step 1806) the snapshotof the content of the logical volume 500. As the method of acquiringsuch a snapshot, for example the technique disclosed in U.S. Pat. No.6,658,434 may be employed. It should be noted that, in this embodiment,just as in the case of the method described in embodiment 1, reflectionof the write data to the volume that stores the snapshot data is stoppedat the time of acquisition of the snapshot, and the content of thevolume that stores the snapshot is frozen. After updating the snapshot,the snapshot acquisition section B 260 reports completion of snapshotupdating to the management software B 890 (step 1807). After confirmingthat a report of completion of snapshot updating has been obtained fromall of the storage devices B 190 that were designated, the managementsoftware B 890 proceeds to the next processing (step 1808, step 1809).

The management software A 800 and the management software B 890respectively repeat the processing of the aforesaid step 1600 to step1613 and of step 1800 to step 1809. In this way, the updating of thestorage device A 100 to the logical volume 500 is constantly reflectedto the logical volume 500 of the storage device B 190.

By processing as described above, the data updating by the MFA 600 andthe open system host A 700 is stopped and a marker is created with thetiming (checkpoint) at which the updating condition is unified betweenthe plurality of storage devices; reflection (i.e. storage) of theupdated data to the stored copy data in the plurality of target logicalvolumes provided in the plurality of target storage devices B 190 can besynchronized at the time immediately preceding the writing of themarker, so mutual consistency between the various copies can be obtainedwith the data of the mainframe host and the data of the open system hostat the time of this marker. In addition, the MFB 690 or open system hostB 790 can continue business using the matched data stored in thesnapshot volume, since a copy having mutual consistency is held in thesnapshot volume, this snapshot being acquired by reflection of theupdated data to the copy data at a time that is synchronized between theplurality of copy data.

In the above processing, the snapshot was assumed to be updated by thestorage device B 190 in response to an instruction from the managementsoftware B 890, but it would be possible to update the snapshot with thetiming of synchronization of reflection of the updated data between thecopy data of a plurality of storage devices B 190. FIG. 20 shows anexample of the reflection processing of write data to the copy in thestorage devices B 190 in this case.

The management software B 890 gives instructions,(step 1900) forreflection of the write data as far as the marker to the logical volumeof 500 that stores the copy in all of the storage devices B 190. Afterreceiving such an instruction, the write data reflection section B 240reflects the write data in the same way as in the processing describedwith reference to FIG. 19 but stops the reflection as soon as it finds amarker and notifies the snapshot acquisition section B 260 (step 1901).After receiving such notification, the snapshot acquisition section B260 updates the snapshot of the content of the logical volume 500 andnotifies the write data reflection section B 240 (step 1902). Afterreceiving this notification, the write data reflection section B 240reports completion of reflection to the management software B 890 (step1903). The management software B 890 confirms that a report ofcompletion of snapshot updating has been obtained from all of thestorage devices B 190 that were designated and then proceeds to the nextprocessing (step 1904, step 1905).

Also, in the aforesaid processing, it was assumed that the storagedevice A 100 or storage device B 190 reported completion of processingin respect of the various types of instructions from the managementsoftware A 800 or management software B 890. However, it would also bepossible for completion of the various types of processes by the storagedevice A 100 or storage device B 190 to be detected by the managementsoftware A 800 or management software B 890 by the management software A800 or management software B 890 periodically making inquiries of thestorage device A 100 or storage device B 190 regarding their processingcondition in respect of the aforesaid instructions.

Also, in the above processing, transfer processing of write data fromthe storage device A 100 to the storage device B 190 is performedcontinuously, but it would be possible for the storage device A 100 tocreate a marker and to then stop transfer of write data and, inaddition, for the storage device B 190, after detecting reflectionprocessing of the received marker (after reflection of the write dataprevious to the marker) to stop reflection of the write data i.e. to putthe processing by the storage device A 100 and storage device B 190 in astopped condition (also called a suspended condition). However, thestorage device B 190 could perform write data reflection up to thedetection of the marker without reference to instructions from themanagement software B 890. In this case, the marker creation instructionis equivalent to an instruction to shift to the, suspended condition andmutually matched copies are created in the logical volume 500 of thestorage device B 190 at the, time where all of the storage devices B 190have shifted to the suspended condition. When restarting the copyprocessing, the copy processing is recommenced by the storage device A100 and storage device B 190 in response to an instruction forrecommencement of copy processing from the management software A 800 ormanagement software B 890 after acquisition of the snapshot of thelogical volume 500. As a result, copies having mutual consistency can beheld in data stored by the snapshots, so MFB 690 or open system host B790 can continue business using the matched data.

Also, in the processing described above, the various types ofinstructions, reports and exchange of information between the managementsoftware A 800 or management software B 890 and storage device A 100 andstorage device B 190 may be executed by way of an I/O path 900 or couldbe executed by way of a network 920. In the case where instructions formarker creation are given in the form of a write request to the storagedevice A 100, a logical volume 500 that is not subject to the processingdeferment of write instructions is provided at the storage device A 100and the marker creation instructions are given in respect of thislogical volume 500.

In the above processing, the storage device A 100 and storage device B190 need not be connected in one-to-one relationship and it is notnecessary that there should be the same number of devices, so long asthe respective logical volumes 500 and logical volume groups correspondas source and copy.

Also, in the above construction, it was assumed that the managementsoftware A 800 was present in the MFA 600 and the management software B890 was present in the MFB 690; however, it would be possible for themanagement software A 800 and management software B 890 to be present inany of the MFA 600, MFB 690, open system host A 700, open system host B790, storage device A 100 or storage device B 190. Also, they could bepresent in another computer, not shown, connected with the storagedevice A 100 or storage device B 190.

In the above processing, it was assumed that the write data reflectionsection B 240 determined the correct marker number, but it would also bepossible for the correct marker number to be designated to the storagedevice B 190 as a parameter of the reflection instructions by themanagement software B. Also, it could be arranged that when themanagement software A 800 gives instructions for deferment of processingof write requests and marker creation to the storage device A 100, aunique marker number is determined and designated to the storage deviceA 100 and communicated to the management software A 890 and that thismanagement software B 890 then designates this marker number to thestorage device B 190.

In the above processing, the occasion at which the management software A800 instructions for deferment of processing of write requests andmarker creation to the storage device A 100 may be determined in amanner linked with the processing of the APP 620 or APP 720. Forexample, synchronization of reflection to the copy may be performed atthe checkpoint by giving instructions for deferment of write requestprocessing and marker creation on the occasion of creation of a DBMScheckpoint. Business can therefore be continued by the MFB 690 or opensystem host B 790 using the data of this condition, by obtaining asnapshot in the condition in which the stored content of the sourcelogical volume 500 at the checkpoint has been reflected to the copy inthe target logical volume.

It could also be arranged for the MFA 600 or open system host A 700 todefer issue of a write request to the storage device A 100 or torestart, by linking the OS 610 or OS 710 with the management software A800, instead of the management software A 800 giving instructions fordeferment of processing of write requests and canceling of deferment inrespect of the storage device A 100.

Also, as described in embodiment 1, a logical volume for write datastorage that is separate from the cache 400 could be prepared and thewrite data stored in this logical volume 500 for write data storage.Also, in the transfer processing of write data, it would be possible fora write data transfer request to be initially issued in respect of thewrite data transfer section 220 by the write data reception section B211 and for the write data to be transferred in respect of the writedata reception section B 211 by the write data transfer section A 220after receiving this request.

The processing described in this embodiment could also be implementedeven if the write request does not contain a write time.

Embodiment 4

FIG. 21 is a view showing an example of the layout of a computer systemin embodiment 4.

The difference with respect to Embodiment 3 lies in that the MFA 600 andthe open system host A 700 are respectively connected with a pluralityof storage devices C 180 by way of an I/O path 900 and the plurality ofstorage devices C 180 are connected with a plurality of storage devicesA 100 by way of a transfer path 910. In addition, the plurality ofstorage devices C 180 are connected with another computer or device bymeans of a network 920. The storage device A 100 and the storage deviceB 190 of embodiment 4 have the same construction and function as thestorage device A 100 and storage device B 190 in embodiment 3.

In this embodiment, just as in the case of embodiment 2, a copy of thedata stored in the logical volume 500 of the storage device C 180 isstored in the logical volume 500 of the storage device A 100.Specifically, the storage device C 180 comprises the same constructionand various types of information as in embodiment 2 and after receivinga write request to the logical volume 500 from the MFA 600 or opensystem host A 700, the storage device C 180 stores the write data thatit has received and transfers this received write data to the write datareception section A 210 of the storage device A 100; however, it is thenguaranteed that a copy of the write data 640 or write data 740 that waswritten by the storage device C 180 exists in the storage device A 100,by sending a write completion notification to the MFA 600 or open systemhost A 700 after waiting for a notification of completion of receptionfrom the write data reception section A 210, in the same way as inembodiment 2.

In addition, a copy of the data stored in the logical volume 500 of thestorage device C 180 is stored in a logical volume 500 of the storagedevice B 190 by the same processing as the processing described inembodiment 3. By processing as described above, as described inembodiment 2, even if for example some fault occurs in the storagedevice C 180 or in the transfer path 910, causing transfer of data tothe storage device A 100 to become impossible, the expected content thatwas recognized as having been stored in the storage device C 180 whenprocessing of the MFA 600 or open system host A 700 was interrupted canstill be obtained from the storage device B 190, so the MFB 690 or opensystem host B 790 can continue business using this data.

In the above processing, the management software A 800 givesinstructions for deferment of processing of write requests or markercreation or cancellation of deferment of processing of write requests inrespect of all of the storage devices C 180 in the same way as in thecase of the processing performed in respect of the storage device A 100in embodiment 3. Just as in the case of step 1600 of embodiment 3, themanagement software A 800 first of all gives instructions for defermentof processing of write requests to all of the storage devices C 180.After receiving these instructions, the write data reception section C212 of the storage device C 180 defers processing of write requests inthe same way as in the case of the processing performed by the storagedevice A 100 in step 1601 and step 1602 of embodiment 3 and reportscommencement of deferment to the management software A 800. As describedabove, at this time, write data in respect of which a write completionnotification has been given in respect of the MFA 600 or open systemhost A 700 has already been transferred to the storage device A 100 andthe storage device A 100 creates write data management information 300of this write data. In the same way as in the case of step 1603 and step1604 of embodiment 3, the management software A 800 confirms that areport of commencement of deferment has been obtained from all of thedesignated storage devices C 180 before proceeding to the followingprocessing.

Next, the management software A 800 gives instructions for markercreation to all of the storage devices C 180 in the same way as in thestep 1605 of embodiment 3. After receiving such an instruction, thestorage device C 180 transmits a marker creation instruction through thepath 910 or network 920 to the storage device A 100 that stores thecopy. After receiving the marker creation instruction, the storagedevice A 100 creates a marker in the same way as in step 1606, step 1607and step 1608 of embodiment 3 and reports completion of marker creationto the storage device C 180 through the transfer path 910 or network920. After receiving the report, the storage device C 180 reportscompletion of marker creation to the management software A 800. Themanagement software A 800 confirms that a report of completion of markercreation has been received from all of the designated storage devices C180 in the same way as in step 1609 and step 1610 of embodiment 3 beforeproceeding to the next processing.

Next, the management software A 800, in the same way as in step 1611 ofembodiment 3, gives instructions for cancellation of deferment ofprocessing of write requests to all of the storage devices C 180. Afterreceiving these instructions, the write data reception section C 212 ofthe storage device C 180 cancels the write request processing defermentin the same way as the processing that was performed by the storagedevice A 100 in step 1612 and step 1613 of embodiment 3 and reports thiscancellation of deferment to the management software A 800.

Specifically, deferment of processing of write requests and cancellationof deferment are performed by the storage device C 180 and markercreation meanwhile is performed by the storage device A 100 ontransmission to the storage device A 100 of an instruction by thestorage device C 180. As described above, write data in respect of whichcompletion of writing has been notified to the MFA 600 or open systemhost A 700 has already been transferred to the storage device A 100 andwrite data management information 300 of such write data is created inthe storage device A 100, so deferment of processing of write requestsby the storage device A 100 in embodiment 3 and deferment of processingof write requests by the storage device C 180 in this embodiment areequivalent. Consequently, by performing processing as described aboveand by performing other processing as described in embodiment 3, in theconstruction of this embodiment, reflection of updating to the copiescan be synchronized at the marker time by stopping data updating by theMFA 600 and open system host A 700 in the same way as in embodiment 3and creating a marker of the updated condition with unified timing(checkpoint) between the plurality of storage devices; mutualconsistency of the respective copies with the mainframe host data andthe open system host data can thus be achieved at this time.Furthermore, mutually matched copies are maintained in snapshot volumesby acquiring snapshots at the time of synchronization of reflection andthe MFB 690 or open system host B 790 can therefore continue businessusing matched data.

In the above processing, it was assumed that the management software A800 gave instructions for marker creation to the storage devices C 180and the storage devices C 180 transmitted these instructions to thestorage devices A 100; however, it would also be possible for themanagement software A 800 to give instructions for marker creationdirectly to all of the storage devices A 100 and for the storage devicesA 100 to report completion of marker creation to the management software800. Specifically, the management software A 800 first of all givesinstructions for deferment of write request processing to all of thestorage devices C 180 and the management software A 800 confirms thatreports of commencement of deferment have been received from all of thedesignated storage devices C 180 before giving instructions for markercreation to all of the storage devices A 180 in the same way as in step1605 of embodiment 3. After having received these instructions, thestorage device A 100 creates a marker in the same way as in step 1606,step 1607 and step 1608 of embodiment 3 and reports completion of markercreation to the management software 800. After confirming that reportsof completion of marker creation have been obtained from all of thedesignated storage devices A 100 in the same way as in step 1609 andstep 1610 of embodiment 3, the management software A 800 may be arrangedto give instructions for the cancellation of deferment of write requestprocessing to all of the storage devices C 180.

Also, it would be possible that the storage devices C 180 are providedwith a marker creation section and marker number information 330 andcreate a marker on receipt of instructions for marker creation from themanagement software A 800; the marker, which has been created as writedata, is then transferred to the storage device A 100 and completion ofmarker creation may be arranged to be reported to the managementsoftware A 800 when a report of receipt thereof has been received fromthe write data reception section 210 of the storage device A 100. Inthis case, the storage device A 100 treats the received marker as aspecial type of write data, which is transferred to the storage device B190 after processing in the same way as ordinary write data except thatreflection to the copy is not performed.

In any case, the above can be implemented irrespective of the number ofstorage devices C 180 that are connected with the storage devices A 100and deposit copies on the storage devices A 100.

Also, although not shown, if a mainframe host and open system host areconnected with the storage devices A 100 by an I/O path, if for examplesome fault occurs in the MFA 600 or open system host A 700 or storagedevices C 180, the aforesaid mainframe host and open system host cancontinue business using the content of the logical volume 500 of thestorage device A 100 that is matched therewith.

1-20. (canceled)
 21. A remote copy system comprising: plural firststorage systems, each comprising one or a plurality of first logicalvolumes, each storing data written from a host computer, a first memory,and a first control section executing a write process based on a writerequest from the host computer, wherein each first control section isconfigured to receive a write request from the host computer, storewrite data received from the host computer to the first memory, send acompletion report to the host computer, and after sending the completionreport, transmit write data stored in the first memory to a secondstorage system; and one or a plurality of second storage systems, eachcomprising one or a plurality of second logical volumes, each storingcopy data of data stored in a first logical volume, a second memory, anda second control section executing a write process to the one orplurality of second logical volumes, wherein each second control sectionis configured to receive write data from a first control section andstore the received write data to a second memory; wherein a marker ID,which is a number that is common across all participating first storagesystems, is provided with each first storage system from the hostcomputer, each first control section is configured to transmit theprovided marker ID to a second storage system, and each second controlsection is configured to store write data, which is stored in the secondmemory to a second logical volume according to the received marker ID.22. A remote copy system according to claim 21, wherein each secondcontrol section is configured to store write data, which is received bya first storage system before the marker ID is provided with the firststorage system.
 23. A remote copy system according to claim 22, whereineach first control section is configured to transmit a marker includingthe marker ID to a second storage system, and the marker is used forspecifying write data, which is received by a first storage systembefore the marker ID is provided with the first storage system.
 24. Aremote copy system according to claim 21, wherein each first controlsection is configured to transmit a marker including the marker ID to asecond storage system, and the marker is used for specifying a set ofdata, which is stored in the second memory and can be stored in a secondlogical volume by each second storage system.
 25. A remote copy systemcomprising: plural first storage systems, each comprising one or aplurality of first logical volumes, each storing data written from ahost computer, a first memory, and a first control section executing awrite process based on a write request from the host computer, whereineach first control section is configured to receive a write request fromthe host computer, store write data received from the host computer tothe first memory, send a completion report to the host computer, andafter sending the completion report, transmit write data stored in thefirst memory to a second storage system; one or a plurality of secondstorage systems each comprising one or a plurality of second logicalvolumes, each storing copy data of data stored in a first logicalvolume, a second memory, and a second control section executing a writeprocess to the one or plurality of second logical volumes, wherein eachsecond control section is configured to receive write data from a firstcontrol section and store the received write data to the second memory;and a first management section, which is configured to issue a defermentinstruction to each first control section of the plural first storagesystems, wherein each first control section is configured to defer awrite process according to the deferment instruction received from thefirst management section, and transmit a marker to a second storagesystem, and each second control section is configured to store writedata from the second memory to a second logical volume according to amarker received from a first control section.
 26. A remote copy systemaccording to claim 25, wherein the marker is used for specifying a setof write data which can be stored from a second memory to a secondlogical volume.
 27. A remote copy system according to claim 26, whereinthe marker is used by a second control section for specifying a set ofwrite data, which is received by a first storage system before the firststorage system receives the deferment instruction.
 28. A remote copysystem according to claim 25, wherein the first management section isfurther configured to check whether each first control section hasdeferred a write process or not, and issue a trigger to each firstcontrol section, and each first control section is further configured toprepare to transmit a marker to a second storage system according to thereceived trigger.
 29. A remote copy system according to claim 28,wherein each first control section indicates ready status to the firstmanagement section, and the first management section checks whether eachfirst control section has deferred a write process or not based on theready status indicated by each first control section.
 30. A remote copysystem according to claim 28, wherein the trigger is a marker createinstruction, based on which each first control section creates a markerto be transmitted to a second storage system, and the first managementsection is further configured to check whether each first controlsection has created a marker or not, and issue a restart instruction toeach first control section to restart a write process in the pluralfirst storage systems after all of the plural first storage systems havecreated a marker based on the marker create instruction.
 31. A remotecopy system according to claim 25, wherein each second control sectionis further configured to acquire a snapshot of the second logicalvolume, in which write data received by a first storage system is storedbefore the first storage system receives the deferment instruction. 32.A remote copy system according to claim 25, wherein the first managementsection is included in the host computer coupled to one of the pluralfirst storage systems.
 33. A remote copy system according to claim 25,wherein the first management section is included in one of the pluralfirst storage systems.
 34. A remote copy system according to claim 25,comprising: plural second storage systems; and a second managementsection which is configured to issue a storing instruction to eachsecond control section, wherein each second control section of theplural second storage systems is configured to store write data, whichis received by a first storage system before the first storage systemreceives the deferment instruction, from the second memory to a secondlogical volume according to the storing instruction received from thesecond management section.
 35. A remote copy system according to claim34, wherein the second management section is further configured to issuea snapshot instruction to each second control section, and each secondcontrol section is configured to acquire a snapshot of the secondlogical volume according to the snapshot instruction received from thesecond management section.
 36. A remote copy system according to claim34, wherein the second management section is included in the hostcomputer coupled to one of the plural second storage systems.
 37. Aremote copy system according to claim 34, wherein the second managementsection is included in one of the plural second storage systems.
 38. Aremote copy system comprising: one or a plurality of first storagesystems, each said first storage system comprising one or a plurality offirst logical volumes, each said first logical volume storing write datafrom a host computer, a first memory, and a first control sectionexecuting a write process based on a write request from the hostcomputer, wherein each first control section is configured to receive awrite request from the host computer, store write data received from thehost computer to the first memory, send a completion report to the hostcomputer, and transmit write data stored in the first memory to a secondstorage system; and one or a plurality of second storage systems, eachcomprising one or a plurality of second logical volumes, each storingcopy data of data stored in a first logical volume, a second memory, anda second control section executing a write process to the one or aplurality of second logical volumes, wherein each second control sectionis configured to receive write data from a first control section andstore the received write data to a second memory; wherein a marker datathat is common across all participating first storage systems isprovided to each participating first storage system, each first controlsection is configured to transmit the provided marker data to a secondstorage system, and each second control section is configured to storewrite data, which is stored in the second memory to a second logicalvolume according to the received marker data.
 39. A remote copy systemaccording to claim 38, wherein each second control section is configuredto store write data, which is received by a first storage system beforethe marker data is provided to the first storage system.
 40. A remotecopy system according to claim 38, wherein each first control section isconfigured to transmit a marker including the marker data to a secondstorage system, and the marker is used for specifying write data, whichis received by a first storage system before the marker data is providedto the first storage system.
 41. A remote copy system according to claim38, wherein each first control section is configured to transmit amarker including the marker data to a second storage system, and themarker is used for specifying a set of data, which is stored in thesecond memory and can be stored in a second logical volume by eachsecond storage system.